Apparatus for monitoring thickness of wall lining of electric arc furnace



H. K. LUNIG 3,532,797 FOR MONITORING THICKNESS OF WALL ING OF ELECTRIC ARC FURNACE Filed Aug. 7, 1967 Oct. 6, 1970 APPARATUS LIN Fig. 1

United States Patent 3,532,797 APPARATUS FOR MONITORING THICKNESS OF WALL LINING OF ELECTRIC ARC FURNACE Hermann K. Lunig, 20 Hohenzollerstrasse, 41 Duisburg, Germany Filed Aug. 7, 1967, Ser. No. 658,737 Int. Cl. F27d 1/00 U.S. CI. 13-1 11 Claims ABSTRACT OF THE DISCLOSURE Apparatus for monitoring the thickness of the wall lining of an electric arc furnace comprises a plurality of electrical conductor loops embedded in the lining, the loops being staggered at successively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness. A source of electric potential is connected through stepping switch means to the loop nearest the initially exposed surface of the lining and, as each loop is destructively melted, the potential source is successively stepped to the loop next nearest the surface of the lining.

The pulses responsive to each such stepping are applied to a second stepping switch means connected to a voltage divider to successively vary the output voltage of the divider, and a recording volt meter is connected to the voltage divider to record the lining thickness.

BACKGROUND OF THE INVENTION A method for monitoring the thickness of the wall lining of electric arc furnaces, and controlling the energy supply to the furnaces, inolves the incorporation of radioactive emitters into the furnace lining. These emitters, upon decrease of the lining thickness due to melting away thereof, decrease their intensity of radiation with respect to a preset value, and the changes in emitted radiation are measured by stationary radiation receivers located outside the furnace. After amplification, these changes are transmitted to an indicating and/or control device by means of which the still existing wall lining thickness is constantly recorded and/or the supply of electrical energy to the furnace is controlled.

A disadvantage of this method and apparatus is the necessity of providing shielding against radioactive radiation in order to protect the furnace operating personnel, and another disadvantage is the relatively high cost of the apparatus, and particularly of the radioactive emitters.

In a known device for indicating, by signals, erosion or melting of the linings of melting crucibles, electrodes are embedded in the wall of the crucible and are separated from each other by means of an electrically conducting insulating layer whose resistance increases with increasing temperature. A potential is applied between the electrodes, and the latter are connected with electrical indicating devices.

The electrodes proper, in this prior art arrangement, consist of two intersecting or cross-groups of wires or metal strips which are spaced from each other and separated from each other, each group being situated on a cylindrical jacket surface. The individual wires of each group are connected, through a signal device such as a signal lamp, and/or through a switching device, to one pole of a source of electric potential.

ICC

Disregarding the fact that this prior art construction requires a very expensive and extensive expenditure for the electrical construction, the arrangement is capable only of indicating relatively early, diiferentially and selectively at which area and to what extent there is a danger of a breakthrough or penetration of the crucible. However, in practice, the best that can be obtained with this prior art device is that the operating personnel is warned in an optical or acoustical manner, so that the operating personnel will empty the crucible to an extent such that the imminent breakthrough area will be situated above the level of the bath in the crucible.

SUMMARY OF THE INVENTION The invention relates to the monitoring of the thickness of wall linings of electric arc furnaces and, more particularly, to an improved, simplified and less expensive apparatus for such monitoring.

In accordance with the invention, instead of radioactive emitters, electrical resistance wires are installed in the furnace lining. Thereby it is not necessary to provide shielding against radioactive radiation, and which otherwise would be necessary in order to protect the furnace operating personnel. By using electrical resistance wires, a very significant saving in cost, with respect to the construction of the furnace, is obtained. Additionally, the electrical resistance wires are much less expensive than the radioactive emitters, while the overall effect is the same.

The present invention goes a significant step further than the mentioned pror art device embodying electrodes embedded in the wall of a crucible. In the present invention, the wires are in the shape of electrical conductor loops and are arranged in the wall lining in a staggered manner so that, upon decrease in the thickness of the lining, the conductor loops are successively destructively melted. By means of current changes due to such destructive melting, signals or control values are generated for recording the remaining thickness of the lining, the lining thickness always being proportional to a respective potential value which is tapped in a voltage divider through stepping switch mechanism. This stepping switch mechanism is, in turn, actuated by relays or the like responsive to the current changes occurring upon destructive melting of a conductor loop portion.

An important feature of the invention is that corresponding ends of all of the conductor loops are connected to a common terminal of a source of potential, while the other corresponding ends of the loops are connected with a stepping switch mechanism of a known design. Resistance is connected in series with the stepping switch mechanism, and has a resistance value preferably larger than that of a conductor loop.

The voltage drop resulting from the resistance actuates a relay or the like, which closes a pair of contacts. Upon melting of a conductor loop portion, when the relay has been actuated, the contacts are opened and, at the same time, the switching mechanism is stepped to the next succeeding conductor loop located inwardly of the conductor loop which has just been destructively melted.

The pulses generated by actuation of the relay step another stepping switch mechanism connected to taps of a voltage divider. The resulting different voltage drops across the voltage divider are transmitted to a recording volt meter which thus records the remaining thickness of the wall lining.

The melting point of the conductor loops should preferably be in the neighborhood of the melting point of the furnace lining. The conductor loops are positioned within insulating tubes which are arranged in a bundle and staggered in depth at spacings of about mm.

The invention arrangement has numerous advantages, among which is the avoidance of expensive switching mechanism. The circuit components necessary for effecting the switching, such as, for example, relays, resistances, stepping switch mechanisms, and the like, are readily available on the market and are of common construction and therefore safe and inexpensive. They permit a simple and inexpensive measuring and recordation of the thickness of the furnace lining.

As compared to known signal devices, a very important advantage of the invention arrangement is that the thickness of the lining is continuously recorded and is indicated by a recording volt meter. Thereby, at any given time, the condition of the wall lining can be read from the recording volt meter. The recording of the lining thickness has the advantage that, without any additional measures, and by way of example, the areas of the lining which are subjected to particular wear and which, in accordance withexperience, are situated about to cm. above the level of the melt, can be charged variable or decreased amounts of energy. Such a variable energy charging is of importance because the Wear of the individual furnace sections differs quite substantially. The wear can thus be equalized to a far-reaching extent by the invention and can, in fact, very often be completely avoided.

Accordingly, an object of the present invention is to provide improved apparatus for monitoring the thickness of the wall lining of an electric arc furnace.

Another object of the invention is to provide such an apparatus in which a plurality of electrical conductor loops are embedded in the lining and are staggered at successively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness.

A further object of the invention is to provide such an apparatus in which, responsive to each destructive melting of the loop, a control signal is provided and is converted into a respective voltage value representing the distance of the destructively melted 100p from the initially exposed surface of the lining.

Still another object of the invention is to provide such an apparatus including stepping switch means, associated relay means, a voltage divider and a recording volt meter for maintaining a continuous record of the thickness of the furnace lining.

A further object of the invention is to provide such an apparatus which simple, inexpensive to construct and inexpensive to install.

Yet, another object of the invention is to provide such an apparatus which is reliable and safe in operation and does not require special equipment to protect personnel.

BRIEF DESCRIPTION OF THE DRAWINGS For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a diagrammatic horizontal section of the wall lining of a metallurgical furnace illustrating conductor loops incorporated in the lining, together with a schematic wiring diagram of the electric circuit means associated with the conductor loops;

FIG. 2 is a diagrammatic vertical section of the wall lining illustrating the insulating tubes which are arranged in staggered and bundled manner; and

FIG. 3 is a diagrammatic front elevation view of the insulating tubes with the conductor loops arranged therewithin.

4 DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the invention, insulating tubes 2 are embedded in the lining 1 of a metallurgical furnace. Tubes 2 are made of a suitable material such as, for example, aluminum oxide (A1 0 or the like. The tubes are bundled into an essentially cylindrical bundle and accommodate the respective metallic conductor loops indicated at 3. The conductor loops may be formed of resistance wire such as that known to the trade as Constantan. Of course, other alloys can be used for the conductor loop provided that their melting point is in the neighborhood of the melting point of the furnace lining so that it is assured that, when the lining liquefies or melts, the conductor loop will also melt.

The tubes 2, each containing a conductor loop portion 3, are staggered as to depth relative to each other and to the initially exposed surface of the lining. For example, the staggering may be at distances of about 10 mm. Thus, when there occurs a wearing away or melting of the lining wall 1, the conductor loop 3 nearest the contents of the furnace will melt first.

The ends 3a of the conductor loops are connected to a suitable source of either A.C. or DC. potential indicated at 4. The other ends 3b of the conductors are connected to respective contacts of a stepping switch mechanism 5 connected in series with an adjustable resistance 6. The resistance value of resistance 6 is normally larger than than that of a conductor loop 3, so that as large as possible voltage drop can be provided across resistance 6. The voltage drop across bias resistance 6 picks up or activates relay 7 to close contacts 7a, 7b of the relay.

If now the conductor loop 3 nearest the exposed surface of the lining, and which is in circuit with the resistance 6, starts to melt, relay 7 is transferred or drops to open its contacts 7a and 7b. Thereby, stepping switch mechanism 5 is stepped to the next contact and the next innermost conductor loop 3 is connected in series with resistance 6. A voltage drop is now present across resistance 6 so that relay 7 is picked up to close contacts 7a and 7b. Upon melting away or destructive melting of the now connected conductor loop 3, relay 7 will again be dropped or transferred to open contacts 7a and 7b resulting in another stepping of stepping switch mechanism 5. This procedure is repeated responsive to increasing wear or erosion of the furnace lining and in correspondence to the number of conductor loops 3 that are present.

In response to the actuation of relay 7, a current pulse is created and is supplied to another stepping switch mechanism 8 whose respective contacts are connected to respective voltage taps of a voltage divider 9. Advantageously, the voltages tapped on the divider 9 are so chosen that each voltage corresponds to a particular thickness of furnace wall lining 1. Upon melting of a conductor loop 3 in the lining 1, stepping switch mechanism 8 will also be stepped by one contact in the same manner as described for stepping switch mechanism 5.

The voltage tapped across voltage divider 9 by stepping switch mechanism 8 is supplied to a recording volt meter or the like 10 which thus continuously records the thickness of the lining 1 and indicates the thickness. The voltage applied across voltage divider 9 and adjustable resistance 11 connected therewith can be obtained from transformer 12, connected to source 4, through full wave rectifier 13. Alternatively, the voltage may be obtained from another source of potential such as, for example, a battery or the like.

By virtue of the apparatus of the invention, which is exceedingly simple in construction and inexpensive, it is possible not only to choose the total value of the voltage of divider 9 so that its magnitude will be as large as possible, but also, by staggering of the conductor loops behind each other, it is possible to' obtain a sufficiently exact measuring and recordation of the lining thickness.

What is claimed is:

1. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as for control of the energy supplied to the furnace, comprising, in combination, a plurality of electrical conductor loops embedded in the lining, said loops being staggered at successively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness; signal generating means including a source of electric potential and circuit components, connected to each loop in succession, one loop at a time, and operable, responsive to each destructive melting of a connected loop, to generate a control signal and to switch to the next succeeding loop; and signal responsive means connected to said signal generating means and to a source of electric potential and operable, responsive to each control signal, to develop a respective voltage value corresponding to the distance of the destructively melted loop, providing the control signal, from the initially exposed surface of the lining.

2. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as claimed in claim 1, including respective tubes of insulating material laterally confining each of said electrical conductor loops.

3. Apparatus for monitoring the thickness if the wall lining of an electric arc furnace, as for control of the energy supplied to the furnace, comprising, in combination, a plurality of electrical conductor loops embedded in the lining, said loops being staggered at successively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness; signal generating means including a source of electrical potential and circuit components, connected to said loops and operable, responsive to each destructive melting of a loop, to generate a control signal; and signal responsive means connected to said signal generating means and to a source of electric potential and operable, responsive to each control signal, to develop a respective voltage value corresponding to the distance of the destructively melted loop, providing the control signal, from the initially exposed surface of the lining; said signal generating means including stepping switch means operable, responsive to each destructive melting of a loop, to connect the next succeeding loop across said first-mentioned source of electric potential.

4. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as claimed in claim 3, in which said signal responsive means includes stepping switch means stepped responsive to each control signal, and a tapped voltage divider connected to said secondmentioned stepping switch means.

5. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as for control of the energy supplied to the furnace, comprising, in combination, a plurality of electrical conductor loops embedded in the lining, said loops being staggered at successively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness; signal generating means, including a source of electric potential and circuit components, connected to said loops and operable, responsive to each destructive melting of a loop, to generate a control signal; and signal responsive means connected to said signal generating means and to a source of electric potential and operable, responsive to each control signal, to develop a respective voltage value corresponding to the distance of the destructively melted loop, providing the control signal, from the initially exposed surface of the lining; said signal generating means including relay means transferred responsive to each destructive melting of a conductor loop to provide a control signal; said signal responsive means including stepping switch means stepped responsive to transfer of said relay means.

'6. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as claimed in claim 5, including a tapped voltage divider having its taps connected to contacts of said stepping switch means 7. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as for control of the energy supplied to the furnace, comprising, in combination, a plurality of electrical conductor loops embedded in the lining, said loops being staggered at sucessively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness; signal generating means, including a source of electric potential and circuit components, connected to said loops and operable, responsive to each destructive melting of a loop, to generate a control signal; and signal responsive means connected to said signal generating means and to a source of electric potential and operable, responsive to each control signal, to develop a respective voltage value corresponding to the distance of the destructively melted loop, providing the control signal, from the initially exposed surface of the lining; corresponding ends of each of said conductor loops being connected to one terminal of said first-mentioned source of electric potential; said signal generating means including a stepping switch having contacts each connected to the other terminal of a respective conductor loop, and including a switching arm; said signal generating means further including a resistance connected in series between said switching arm and the other terminal of said firstmentioned source of electric potential, the ohmic value of iaid resistance being larger than that of said conductor oops.

8. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as claimed in claim 7, in which said signal generating means includes a relay having an operating coil connected across said resistance and having contacts normally closed when a voltage drop is present across said resistance; said'relay, responsive to destructive melting of a conductor loop, being deenergized to open its contacts to step said stepping switch.

9. Apparatus for monitoring the thickness of the wall lining of a electric arc furnace, as claimed in claim 8, in which said signal responsive means includes a second stepping switch in circuit connection with said relay contacts and stepped responsive to each closing of said relay contacts; said signal responsive means further including a tapped voltage divider having its taps connected to the contacts of said second stepping switch; said second-mentioned source of potential being connected across said tapped voltage divider; and a recording volt meter connected between one end of said voltage divider and the movable arm of said second stepping switch.

10. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as claimed in claim 1, in which the melting point of said electrical conductor loops is of the order of the melting point of the furnace wall lining.

11. Apparatus for monitoring the thickness of the wall lining of an electric arc furnace, as for control of the energy supplied to the furnace, comprising, in combination, a plurality of electrical conductor loops embedded in the lining, said loops being staggered at successively greater distances from the initially exposed surface of the lining so as to be successively destructively melted upon decrease in the lining thickness; signal generating means, including a source of electric potential and circuit components, connected to said loops and operable, responsive to each destructive melting of a loop, to generate a control signal; and signal responsive means connected to said signal generating means and to a source of electric potential and operable, responsive to each control signal, to develop a respective voltage value corresponding to the distance of the destructively melted loop, providing the control signal,

7 8 from the initially exposed surface of the lining; and re- 3,078,707 2/1963 Weaver 7386 X spective tubes of insulating material laterally confining 3,307,401 3/1967 Bachman 73-86 X each of said electrical conductor loops; said tubes being 3,357,237 12/1967 LeBel 340421 X bundled into a substantially cylindrical bundle and staggered as to their depths in the lining, by distances of sub- 5 BERNARD GILHEANY, Primary Examiner stantiany lomm- R. N. ENVALL,JR., Assistant Examiner References Cited UNITED STATES PATENTS US. Cl. X.R.

2,915,305 12/1959 Craig 7386X 10 13-35;73-86;32471;340421 

